Observation of the lowest A_g excited state lying in the optical gap in polydiacetylene by means of second-harmonic generation spectroscopy

详细信息    查看全文

• 作者：Manaka ; Takaaki ; Yamada ; Toshiki ; Hoshi ; Hajime ; Ishikawa ; Ken ; Takezoe ; Hideo
• 关键词：Second-harmonic generation spectroscopy ; Polydiacetylene ; Forbidden excited state
• 刊名：Synthetic Metals
• 出版年：1998
• 出版时间：June 15, 1998
• 年：1998
• 卷：95
• 期：2
• 页码：155-158
• 全文大小：324 K

文摘

We have observed second-harmonic generation (SHG) spectra in polydiacetylene (poly [5,7-dodecadiyne-1,12-diyl-bis-ethylurethane], PDA-4U2 for short) films of red and blue forms. In addition to resonant peaks located at the high-energy side of the main absorption peak, a new resonant peak was observed at the lower-energy side of the absorption peak in blue-form PDA-4U2. In contrast, in red-form PDA-4U2, the SHG resonance peak position in the lower-energy side coincides with the absorption peak position. The resonance enhancement of SHG originates from the electric-quadrupole transition to the dipole-forbidden state. The lowest resonance peak observed in the blue-form PDA-4U2 strongly suggests the existence of the lowest A_g excited state lying below the lowest B_u excited state.